1. Field of the Invention:
The invention relates to a charge-coupled device, and more particularly to a CCD which is especially suited for use as a light sensor; and to a method of making the same.
2. Description of the Prior Art:
Charge coupled elements are known components in semiconductor technology (see, for example, Siemens Forschungs- and Entwick-lungsberichte, Vol. 4, 1975, pages 226 ff; German OS No. 2,201,150). It is further known that charge coupled elements can be used as light sensors (see, for example, "IBM Tech. Disc. Bull.", Vol. 16, No. 1, June 1973, pages 173--174 and "Bell System Technical J1.", Oct. 1972, pages 1923-1926). CCD circuits of this type fundamentally consist of a series of MIS capacitors, each of which MIS-capacitors are constructed in such manner that on the surface of a semiconductor substrate there is applied an electrical insulating layer which bears an electrode. CCD-components of this type can be used, for example, as a store or as radiation sensors for light. At least in each MIS-capacitor, a radiation-transmissive point must be provided in the electrode through which radiation can penetrate into the substrate. The radiation produces change carries in the substrate. When an appropriate voltage is connected between the substrate terminal of the element and the relevant electrode of a MIS-capacitor, these charge carriers can be accumulated in this capacitor in the substrate beneath the capacitor electrode. When sensors of this kind are used to record very weak radiation intensities, it proves disadvantageous that the radiation which, in the sensor, produces the pairs of charge carriers required for recording, must pass through electrodes of such a MIS-capacitor and through the insulating layer into the semiconductor, as both in the electrode and the insulating layer a part of the radiation is already absorbed and thus is no longer available for the production of charge carriers in the semiconductor substrate.
The aim of the invention is to provide a CCD which can be used as a charge store or as a radiation sensor (e.g., for light or ionizing radiation) and which can be used even with weak radiation intensities. As a result of its design, it obviates the need for radiation which forms the pairs of charge carriers to pass through one of the electrodes of this CCD.